js if is undefined code example
Example 1: javascript if undefined
if(typeof comment === 'undefined') {
alert('Variable "comment" is undefined.');
} else if(comment === null){
alert('Variable "comment" is null.');
}
Example 2: javascript check if null
if (variable === null) { //Executes only if variable is null but not undefined
//Code here
}
if (variable == null) { //Executes if variable is null OR undefined
//Code here
}
Example 3: javascript check if undefined or null
// simple check do the job
if (myVar) {
// comes here either myVar is not null,
// or myVar is not undefined,
// or myVar is not '' (empty string).
}